A typical silent chain comprises alternating guide rows and non-guide rows, each comprising a set of link plates. The link plates of the guide rows and the link plates of the non-guide rows are disposed in interleaved relationship.
Each guide row is composed of a pair of spaced, opposed, guide plates and a set of intermediate link plates disposed between the guide plates. The intermediate link plates are engageable with sprockets of a transmission. Each of the non-guide rows is composed of a plurality of inner link plates, which are interleaved with the intermediate link plates of the guide rows and also engageable with the sprockets. Pairs of connecting pins are provided for each pair of guide plates. In the silent chain, the guide rows and non-guide rows are connected in articulating relationship by the connecting pins. A typical silent chain is described in U.S. Pat. No. 6,325,735, granted on Dec. 4, 2001.
In the operation of a silent chain transmission, the condition of the chain changes in various ways. In particular, the chain tends to move laterally, or “swing” in the direction of its width. This movement is sometimes referred to as “lateral swing.”
As shown in FIGS. 9A and 9B, a silent chain 501 comprises guide rows 502, each composed of a pair of guide plates 503 and intermediate link plates 504, non-guide rows 505, each composed of a plurality of inner link plates 506, and pairs of connecting pins 507 fixed to the guide plates 503.
When lateral swing occurs, if an inner end face 503a of a guide plate 503 is located in the vicinity of an engagement starting point 504p, at which an inner flank 504a of an intermediate link plate 504 starts to engage a sprocket tooth 509, it is possible for the guide plate 503 to contact the sprocket tooth 509 before the intermediate link plate 504 contacts the sprocket tooth. Furthermore, as shown in FIGS. 10A and 10B, when a non-guide row 505 starts to engage the driving sprocket 508, lateral swing can result in contact between an end surface 503b of the guide plate 503 and a sprocket tooth 509 before the inner link plate 506 contacts the sprocket tooth.
Ordinarily, the sprocket tooth 509 starts to engage the intermediate link plates 504 and the inner link plates 506 without contacting a guide plate 503. However, if the sprocket tooth 509 contacts the guide plate 503 before it contacts an intermediate or inner link plate, frictional loss and noise are generated due to contact between the guide plate 503 and the sprocket tooth 509, causing deterioration in the performance of the silent chain.
Furthermore, as shown in FIG. 11, when tension in the silent chain 501 increases, the inner link plates 506 can bend the connecting pins 507, which are held by the pair of guide plates 503 one of which is shown in FIG. 11. Bending of the connecting pins 507 can occur when the tensile hardness of the guide plate 503 between the pair of connecting pins 507 exceeds the bending rigidity of the connecting pin 507.
Bending of the connecting pins 507 causes the guide plates 503 to warp so that they become convex toward the intermediate link plates 504 in the chain width direction. Due to the warp, an inner link plate 506 contacts an inside surface 503a of the guide plate 503, causing still more frictional loss when a non-guide row 505 turns relative to an adjacent guide row 502 about the centerline of a connecting pin 507 as the intermediate link plates 504 or the inner link plates 506 start to engage a sprocket.
As shown in FIGS. 9A and 9B, if the back surfaces 503b, 504b and 506b of the guide plate 503, the intermediate link plate 504 and the inner link plate 506 are co-planar, the contact area of the back of the chain with the sliding-contact surface of a chain guide (not shown) increases, resulting in an additional frictional loss.
The several frictional losses described above reduce the power-transmitting efficiency silent chain 501. Accordingly, there is a need for a silent chain having a plate configuration that reduces frictional losses and improves power transmitting efficiency and noise performance.